Online search, I would guess? There are so many learning methods and subjects that I can't really give you one single master plan, but I can say that I've used textbooks, correspondence courses, online courses, community college courses, PSAT, SAT, AP, CLEP, etc. You're probably looking for information specifically on online courses, judging from your PM, and I can say that the online courses I took that were the best were the sort with a high degree of interaction - everyone commenting on everyone else's work, maybe real-time chat at certain times each week, that sort of thing. Courses where you basically just post your work, get a grade, and move on are the same as correspondence courses, and I don't particularly like correspondence courses. But then again, I enjoy competition, so maybe other people might have a different opinion.

Note - if you're writing a paper, or doing product research for a company, please state that up front. If I had to guess, I'd say it's the latter.